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Metal Edge, Inc. 2007 RaT. 



^HE INSTALLATION OF DUST-COLLECTING 
FANS ON THRASHING MACHINES FOR THE 
PREVENTION OF EXPLOSIONS AND FIRES 
AND FOR GRAIN CLEANING 



By 

H. E. ROETHE, Jr., Assistant in Grain Dust Explosion 

Prevention, Bureau of Chemistry, and E. N. BATES, 

Investigator in Grain Handling, Bureau of Markets 




UNITED STATES DEPARTMENT OF AGRICULTURE 
DEPARTMENT CIRCULAR 93 



Contribution from the Bureau of Chemistry, Carl L. Alsberg, Chief 
arid the Bureau of Markets, George Livingston, Chief 



Office of Grain Dust Explosion Prevention 
Bureau of Chemistry 

DAVID J. PRICE, Engineer in Charge 



Washington, D. C. 



May. 1920 



WASHINGTON: GOVERNMENT PRINTING OFFICE: 1920 



MoaograjJ* 



PREPARE FOR THE NEXT THRASHING SEASON. 

Protect thrashing machinery and grain against DUST EXPLOSIONS 
AND FIRES by the installation of — 

1. An effective dust-collecting fan. 

2. An approved type of fire extinguisher. 

3. A wiring system for the removal of static electricity. 

Further information concerning the various phases of this work can 
be obtained from the following bureaus of the United States Department 
of Agriculture, Washington, D. C. — 

Dust Explosion and Fire Prevention, Bureau of Chemistry. 

Grain Cleaning at Time of Thrashing by Fans and Aspirators, 

Bureau of Markets. 
Smut Control Problems, Bureau of Plant Industry. 



WECEIVE0 

NOV 1 ? 1933. 

DIVISION OF 00CUM£MTS 



sj \a i / 



THE INSTALLATION OF DUST- COLLECTING FANS 



ON THRASHING MACHINES FOR THE PRE- 
VENTION OF EXPLOSIONS AND FIRES 
AND FOR GRAIN CLEANING. 



THRASHER EXPLOSIONS AND FIRES IN THE PACIFIC 
NORTHWEST. 

EACH thrashing season costs southeastern Washington and the ad- 
joining sections of Idaho and Oregon from $15,000 to $75,000 in 
machinery and grain destroyed by preventable explosions and fires 
in thrashing machines. This loss, which may seem insignificant in 
comparison with the $1,000,000 damage resulting from the same 
cause in 1914 and 1915, is still serious enough to demand of every 
thrasherman in that section careful consideration of the means for 
preventing such disasters in the future. Investigations of explosions 
and fires in thrashing machines, which were begun in 1914 by the 
Bureau of Chemistry and the Bureau of Public Roads, 1 were con- 
tinued in the Pacific Northwest during the seasons of 1917, 1918, and 
1919 cooperatively by the Bureau of Chemistry, the Bureau of Mar- 
kets, and the Bureau of Plant Industry, of the United States Depart- 
ment of Agriculture. During the season of 1918 the work was ex- 
tended to other grain-growing sections of the country. 

DUST-COLLECTING FANS. 

Of the various devices developed by the United States Department 
of Agriculture for the prevention of grain and smut dust explosions 
and fires in thrashing machines, special dust-collecting fans designed 
for installation on the machines have been found to be effective in : 

1. The prevention of explosions and fires in thrashing machines, 
by collecting the dust from the interior of the separators, thus pre- 
venting the formation therein of explosive mixtures of smut or grain 
dust and air. 

2. The cleaning of grain, particularly of smut, as an economic fea- 
ture in grain handling because of its effect on the grading of wheat 
under the Federal standards (grades). 

3. The control of the wind dissemination of smut spores. 

In addition, these fans materially improve working conditions 
about the machine. 

Such fans should be installed on as many grain separators as pos- 
sible, particularly in the Pacific Northwest, and in all other grain- 
growing sections where bunt or stinking smut of wheat is prevalent. 

'U. S. Dept. Agr. Bui. 379. 
1714S3°— 20 3 



4 Department Circular 98, U. S. Dept. of Agriculture. 
DESIGN, CONSTRUCTION, AND INSTALLATION OF FANS. 

GENERAL POINTS. 

Because of the peculiar and characteristic construction of the 
various makes of thrashing machines it is impossible to give detailed 
specifications of a fan installation adaptable to all types of grain 
separators. Details of construction and the method of attachment 
of equipment vary with each machine. In the selection and in- 
stallation of dust-collecting fans, special attention should be given 
to many important features. Extensive investigations and experi- 
ments have shown that to be most effective and satisfactory such 
equipment for thrashers should embody as many as possible of the 
following general points of design and construction. 

1. A centrifugal-type, steel-plate exhaust fan is most desirable. 

2. A single-inlet-type fan has the advantage of offering the least 
obstruction to the deck. 

3. The fan drive should be as direct as possible from the cylinder 
shaft. The fan pulley should be as large as practicable to prevent 
undue slippage of the belt. A minimum diameter of 4 inches is 
suggested. 

4. A light-running fan, of simple but rigid construction, securely 
attached to the frame of the separator, answers the purpose best. 

5. Ample exterior bearings should be provided, with no overhang 
of the shaft. 

6. For medium-sized machines, ranging from 26 by 46 inches 
to 32 by 54 inches, the fan should have a peripheral speed of ap- 
proximately 6,500 feet per minute, with a capacity, under field con- 
ditions, of from 35 to 40 cubic feet of air per second. These values 
would be slightly greater for the larger and slightly less for the 
smaller machines. With fans of different sizes the revolutions per 
minute may be varied to obtain the constant peripheral speed sug- 
gested. Based on these figures, a fan of average size, 21 inches in 
diameter from tip to tip of vanes, should run at a speed of approxi- 
mately 1,200 revolutions per minute. The same results could be 
secured with a larger fan operated at a lower speed or with a 
smaller one operated at a higher speed. The smaller fan, of course, 
has the advantage of occupying less space. The air resistance of 
such a fan operating under general thrashing conditions would 'be 
a pressure of approximately two ounces. Because of the many 
variables which enter into the operation of a fan, it obviousl} 7 is 
almost impossible to give definite information on this subject. 

7. The eye or inlet of the fan should be located opposite the fan 
pulley at the center of the casing. The discharge pipe should have an 
area at least as great as that of the inlet. 



Dust-Collecting Fans. 5 

8. To collect dust and other light foreign material from the sepa- 
rator most effectively without removing the heavier particles, a fan 
must handle or remove a large volume of air with a very gentle 
movement at the intake, the velocity of the air increasing as it ap- 
proaches the inlet or eye of the fan. This condition is produced by 
means of a tapered intake of large area at its base. 

9. The intake hood should be tapered and the intake should cover 
a deck area of not less than 600 square inches. 

10. The intake should be centered and placed at a forward posi- 
tion on the deck. On most machines this location would be over 
the beater. 

11. If straw, grain, or other heavy material is thrown upward into 
the fan intake by the beater or cylinder of the separator, it will be 
necessary to place a deflection plate or baffle board, preferably me- 
tallic, under the intake at an angle of approximately 30° with the 
deck. 

12. The absence of sharp, abrupt curves or bends in the intake 
and connecting parts is most important. Elbows of all piping should 
have an ample sweep or radius. If possible, no turn in an air pipe 
should be made with a radius of less than twice the pipe diameter. 

13. The least possible obstruction should be offered by the fan 
equipment to the deck and to the interior of the machine through 
the deck doors. 

14. The fan discharge should be conducted through a metal pipe 
to the rear of the separator ; thence by a canvas tube into the base of 
the straw stack. Such an arrangement greatly reduces the wind 
dissemination of, and subsequent soil infestation by, smut spores 
which otherwise would be blown into the air. 

15. If two or more discharge pipes are united, the cross-sectional 
area of the final common pipe should be approximately equal to the 
combined cross-sectional area of the original pipes. Otherwise the 
efficiency of the fan is greatly impaired. 

VARIOUS TYPES OF FAN INSTALLATIONS. 

During the past few years various thrashing-machine companies 
have manufactured and installed, at the suggestion of the United 
States Department of Agriculture, special fan equipment on nu- 
merous machines operating principally in the Pacific Northwest. 
Investigations have been conducted at these machines to determine 
the effectiveness of, and to make every possible improvement in, the 
different fan installations. A number of the most effective and satis- 
factory types of these fans are shown and discussed in the following 
pages. 



Q Department Circular 98, U. S. Dept. of Agriculture. 

1 . A single-inlet fan, having a diameter of 30 inches and a peripheral width 
of 6 inches (outside dimensions), installed on a 32 by 54 inch separator 
(fig. 1). — This fan is admirably driven directly from the cylinder 
shaft at a speed of 1,000 revolutions per minute, and the whole equip- 
ment is well constructed and rigidly attached to the separator frame. 




FlGDRK 1. 



The two intakes, one over the cylinder, the other above and just 
back of the beater, should be noted. A metal deflection plate placed 
directly under the front intake, at an angle of about 30° with the 
deck, prevents the cylinder from throwing into this intake any 
straw, grain, or other heavy material. This fan removes large 
quantities of dust, mainly through the rear intake. The equipment 
would no doubt be more effective if the front intake were eliminated, 
the rear intake enlarged and moved forward slightly, and the intake 
hood built along pyramidal lines, with no sharp, abrupt curves. 



Dust-Collecting Fans. 7 

2. A three-fan installation, consisting of a double, built-in fan with a 
single shaft, located over the beater, and a single fan placed midway on the 
deck of a 23 by 36 inch separator (fig. 2). — Each unit of the double fan 
has one inlet, while the single fan is provided with two inlets. Each 
fan has a diameter of 18 inches and a peripheral width of G inches 
(outside dimensions). The speed of each fan is 1,000 revolutions per 
minute. The single fan is driven from the double fan shaft, which in 
turn is driven from the shaft of the first beater. 




4W? 

mm 




Figure 2. 

This equipment collects large quantities of dust. Doubtless equally 
as satisfactory results could be obtained in a more economical 
manner by removing the single fan and increasing the speed of the 
double fan to approximately 1,200 revolutions per minute. In the 
union of the three discharge pipes shown, the final or common dis- 
charge pipe should be enlarged so that its cross-sectional area would 
approximately equal the combined cross-sectional area of the original 
pipes. Otherwise the fans will not operate at their maximum effi- 
ciency. 



8 Department Circular 98, U. S. Dept. of Agriculture. 




Figure 3. 

3. A 28 by 44 inch separator equipped with a single-inlet fan with 
a diameter of 26 inches and a peripheral width of 6 inches (outside dimen- 
sions (figs. 3, 4, and 5). — The entire fan equipment is constructed of 
metal. The fan is driven from the cylinder shaft at a speed of 1,300 
revolutions per minute. 

The noteworthy features 
of this type of installation 
are (1) the large tapering 
intake over the first beater, 
(2) the rigid construction 
and attachment of the equip- 
ment, (3) the belt tightener 
for starting and stopping' the 
fan, and (4) the movable 
joint at the end of the fan- 
figure 4. discharge pipe. 

4. A double-inlet metal fan 
with tapered intakes located 
over the beater on a 20 by 32 
inch machine (fig. 6). — This 
fan is run at a speed of 900 
revolutions per minute and 
has a diameter of 23 inches 
and a peripheral width of 8 
inches (outside dimensions). 
This equipment shows good 





Dust-Collecting Fans. 



9 



design and construction, but would be more effective if driven from 
either the cylinder or the beater shaft at a speed of about 1,200 revo- 
lutions per minute, vrith a driven pulley at least 4 inches in diameter. 

A metal deflection plate beneath the two in- 
takes, placed at an angle of approximately 30° 
with the deck, prevents clogging of the fan 
with straw, grain, and other heavv material. 




Figure 6. 

5. A wooden, 22J by 12 inch, (outside dimensions of drum) fan installed 
over the second beater on a 36 by 60 inch separator (figs. 7 and 8). — -The 




Figure 7. 
fan is driven from the cylinder shaft at a speed of 1.300 revolutions 
per minute. 



10 Department Circular 98, U. S. Dept. of Agriculture. 




Figure 8. 



This former double-inlet, box-type fan was changed to a single- 
inlet type, the following alterations being made: The fan shaft 
was shortened, one intake and hood removed, and the fan was moved 
to the side of the deck. The remaining intake hood or box was 
tapered and the single inlet in the fan drum was enlarged. The 




FlGUUE 9. 



speed of the fan was increased from 900 to 1,300 revolutions per 
minute. This simply constructed, light-running fan removes large 
quantities of dust. The straight metallic discharge pipe offers very 
little resistance to the passage of the dust-laden air. 



Dust-Collecting Fans. 



11 



Attention is called to the dual fire extinguishing system, consisting 
essentially of a chemical fire extinguisher on the deck and a steam 
hose line running to the steam engine. Each unit is connected to 
a piping system, by means of which the interior of the separator 
is sprayed in case of an explosion or fire. 

6. A wooden, double-inlet, box-type fan, with a 22J by 10 inch drum 
(exterior dimensions), placed over the beater on a 36 by 56 inch sepa- 
rator (fig. 9). — This fan is driven from the beater shaft at a speed of 
800 revolutions per minute. 

Attention is di- 
rected to the idle 

pulley on the fan 
which serves to start 
and stop the fan. 
M o r e satisfactory 
results could be 
obtained with this 
fan by running it 
at a speed of about 
1,200 revolutions 
per minute. The 
alterations de- 
scribed on page 
10 probably could 
be applied to this 
fan to good ad- 
vantage. Wooden 
fans of this type 
are inexpensive and 
light running. 

7. A remodeled 
box - type fan (fig. 
10).— The fan 
case was slightly 
raised and securely 
placed on a rigid 
base. The speed 
was increased to 
approximately 1,200 revolutions per minute. 

The overhang of the fan shaft was remedied by supplying an 
additional bearing near the pulley, while the fan outlet was enlarged 
at the casing. The short section of the metallic discharge pipe was 
equipped with an adjustable 15° elbow. These modifications greatly 
increased the efficiencv of the fan. 




Figure 10. 



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